Ultrasonic sensors are known in which a diaphragm is excited to vibration by ultrasonic waves. The sound waves are converted to an electrical signal by an electroacoustic transducer, for example a piezoelectric element, enabling the signal to be evaluated. In particular when used outdoors, the operation of the ultrasonic sensor may be impaired at low temperatures, for example by ice or snow, if the diaphragm of the ultrasonic sensor is covered thereby. The sound may be absorbed by snow. An ice covering may reduce the diaphragm's ability to vibrate. Furthermore, the ice covering on other components may also cause sound waves to become decoupled, so that the system sensitivity as a whole is reduced. An ultrasonic sensor which is inserted into a holder is described in U.S. Pat. No. 6,282,969. The holder includes a heating element which is used to heat the ultrasonic transducer and, in particular, also the diaphragm. Ice and snow, which may accumulate in front of the ultrasonic sensor holder, are melted thereby.